Carbon dioxide (CO2) is a colorless, odorless gas that can be used as an inert material, as pressurized gas, in “dry ice”, liquid or supercritical fluid applications, and many other areas, such as, for instance, oil production and the chemical industry. In the food sector, CO2 is a medium for decaffeination and a feedstock for obtaining carbonated beverages, providing effervescence to water, soft drinks, wine, beer and so forth. Applications such as found in the beverage industry require CO2 of a specified purity. It is important, therefore, to monitor the nature and levels of contaminants in the gas employed.
Some existing systems for analyzing impurities in CO2 gas rely on gas chromatography (GC), with photoionization detection (PID) and/or flame ionization detection (FID). GC systems, however, can be slow, requiring several (e.g., 6-8) minutes between samples.
Other approaches rely on mass spectrometry (MS), a technique that is fast but can suffer from cross interferences and calibration issues. As with other MS systems, continued maintenance is often required.
Specialized instrumentation geared toward detecting a particular contaminant (total sulfur, for instance) or a class of contaminants (e.g., aromatics) also have been developed. This approach, however, provides limited information. A sensor designed to focus on aromatic compounds, for instance, may fail to signal the presence of acetaldehyde or nitrogen oxides (NOx). One or more additional devices might be needed to analyze for other contaminants. Combining multiple instruments, however, can result in cumbersome calibrations and extensive maintenance.